Russian fighter jets are practicing attacking NATO ships in the Black Sea in another dramatic sign that tensions over Ukraine continue to build despite a fragile ceasefire agreed last month.

“Russia’s newest Su-30 fighter jets and Su-24 attack bombers are using two NATO ships in the Black Sea to practice penetrating anti-air systems,” reports Sputnik, citing a source at the Sevastopol naval base.

Asserting that the NATO ships are conducting drills based around “repelling air attacks,” Moscow is taking the opportunity to practice “maneuvering and conducting aerial reconnaissance” outside the range of the ships in order to “practice attack scenarios”.

The report also states that Russia is closely monitoring the movements of the ships, namely the USS Vicksburg missile cruiser and the Turkish TCG Turgutreis frigate, and the assignments they are performing.

Three Su-30 jets and four Su-24 bombers carried out reconnaissance on the ships yesterday.

The exercises coincide with an unannounced test of nuclear weapons near the central Russian city Yoshkar-Ola. Russia’s Strategic Missile Forces (SMF) said the exercise was based around an assessment of the “condition and security provisions” of nuclear weapons in the Yoshkar-Ola Missile Unit, which is armed with the Topol intercontinental nuclear-capable ballistic missile complex.

Russia has also sought to demonstrate its military might with a series of maneuvers over sovereign European airspace. The latest incident involved two Tu-95 ‘Bear’ long-range strategic bombers which flew 40 kilometers off the Irish coast with their transponders turned off, forcing air traffic control to re-route commercial flights to avoid a collision.

Sporadic fighting in eastern Ukraine between pro-Russian rebels and Kiev forces continues to be reported despite an agreement from both sides to withdraw heavy weapons from the region. At least 6,000 people have been killed since the conflict erupted last year.